Abstract: Method and apparatus for determining (i.e., proving) the accuracy of a gas flow meter includes the use of a flow determining valve to derive flow data representative of actual gas flow rate simultaneously with similar flow data obtained from the meter. Real time quantitative analysis of the gas stream constituents is employed during meter proving (as may be accomplished with an automated gas chromatograph) so as to condition the flow data obtained from the flow determining valve and hence provide a more accurate determination of actual gas flow rate. This conditioned flow data is then compared to the flow data obtained from the meter to thereby derive a variance factor for the meter at given sensed flow rates. Therefore, flow rate data obtained from the meter may then be adjusted as a function of the derived variance factor so that a more accurate determination of actual flow rate through the meter is possible.